[Arran]

 Graphite is carbon, and carbon is one of the substances they make resistors from, so I would be reluctant to use in anywhere in a higher voltage electrical device such as a tube radio. This reminds me of the J.B Weld everything crowd on the alternative forum, J.B is metal filled, do you really want to use that on a tube socket or a switch, especially a band switch?
 I think that the main issue with the popping is that the plates in the tuning cap are rubbing just slightly, or there is crude on the wiper, or there is an issue with a grounding braid/strap such as it has a bad connection to ground or that it's rubbing against the rotor. Since the rubber mounts are probably shot anyhow you might as well remove the tuning cap and clean it.
Regards
Arran